Nuclear transplantation: We plan to explore the possibility that nuclei may be "re-programmed" by changing the types of proteins they contain. This may be done by injecting well characterized proteins into eggs to see whether development is affected through an effect on the zygote's chromosomes; or by exposing somatic cell nuclei to the proteins and then transplanting them into enucleated eggs. Effect of the d gene on pigment cell motility: This problem will be pursued further by means of the following types of experiments. a) Histochemical staining for hyaluronic acid and chondroitin sulfate, to determine whether there are differences in the presence or distribution of these substances in d/d and D/- embryos. b) Scanning electron microscopy of cryofractured specimens. This procedure will be applied to embryos carrying reciprocal grafts of white (d/d) and dark (D/-) epidermis to determine whether there is a strict correspondence in one and the same animal between absence of pigment cell migration and presence of an altered subepidermal matrix. c) Identification and localization of fibronectin. The fibrillar meshwork in the subepidermal space is thought to be fibronectin on the basis of its appearance and its relationship to neural crest cells. Whether it actually is fibronectin, and whether it differs in white and dark embryos, will be explored by immunochemical means.